It's a line that would reverberate through the actor's head just two days after he delivered it. With film cameras trained on him, Butler, 42, was bobbing in Northern California's Half Moon Bay when a massive swell crashed over him, ripping away his surfboard and pinning the actor underneath the churning sea. Lungs burning and quickly losing breath, seconds clicked slowly by as a thought crossed Butler's mind: "Why was this necessary?"

Chasing Mavericks (out Friday) is based on the true story of Jay Moriarity, a fearless young surfer who gained worldwide attention surfing a big-wave mecca near Santa Cruz known as Mavericks. Butler plays Frosty Hesson, Jay's rugged, real-life mentor who schools Jay (played by Jonny Weston) on the rules of survival around 50-foot swells.

Underwater, "all of those things were going around my head, going 'This is it. If I panic now‚?¶" Butler was barely able to gasp a breath before a second wave hit and the cycle began again.

Submerged again, Butler fought the urge to scream. "I felt very present. There was something that felt very normal about it. But by the time I got to the point I got to thinking, 'I'm in big trouble now,' that was only a about a quarter of the way through it. It went on and on and on. And then I started thinking, I just wanted to scream. And I was so deep underwater. I wanted to scream 'Help, somebody!' Or 'Mom!' Or something. And yet I knew the second I did that I was done."

Close to being jettisoned onto jagged rocks, Butler finally grabbed a crew member's hand, was pulled to shore and taken to the hospital (he was released the next day).

It wasn't the first time he'd taken a beating in the ocean.

For months, Butler, whose strength has been showcased in brawny films such as 300 and Law Abiding Citizen, trained with surfing pro (and film consultant) Grant Washburn in Santa Cruz, where Moriarity, at only 16, had attracted worldwide attention in 1994 by wiping out spectacularly on a 30-foot Maverick -- and immediately continuing to surf. The shot was captured on film and landed him on the cover of Surfer magazine.

Beloved by the surfing community for his positive attitude and daredevil skill, Moriarity's resulting career brought greater attention to his sport until his death in 2001 after drowning while free-diving in the Maldives.

"His story, his persona, what he represented was just a huge inspirational tale for surfers and for non-surfers," says Washburn, who surfed with Moriarity.

By all accounts, Butler threw himself into Frosty and Jay's surf, but the waves that were waiting were beasts.

Dangerous days were frequent. "He and I would personally have some sessions where there was nobody else around, it was just the two of us and he got completely smashed like that where he was held down and it was black water," says Washburn.

"That's what grabbed me about the script is understanding the essence of what you go through in that training and that preparation," says Butler who executive-produced the biopic. "I thought I'd never really seen that in a movie, to try and get across how treacherous it is to be out there and then to actually feel that."

Famous big wave surfers like Greg Long, donning hoods that allowed for computer-generated face replacement, filled in for more intense surfing sequences, with up to eight cameras and a helicopter capturing the action.

"Most of the time we were reining (Butler) in," adds Washburn. "We'd be out in the water and he'd get excited, we'd be like 'Slow down!' He really just wants to dive right into the middle of it."

A softer side of 'Gerry'

Despite his penchant for bicep-bulging, bulletproof films (see: Machine Gun Preacher, Gamer), in Chasing Mavericks the only ammo his character is equipped with is verbal, as he takes on a fatherly role mentally and physically preparing young Jay for the surf.

In December, Butler switches over to soccer in Playing for Keeps, a romantic drama directed by Gabriele Muccino (The Pursuit of Happyness) about a retired sportsman trying to forge a relationship with his young son and ex-wife (Jessica Biel).

Butler has worked with Jennifer Aniston (The Bounty Hunter) and Katherine Heigl (The Ugly Truth), but his chemistry with Biel is palpable as his character struggles to hold on to a life outside the all-too-forgiving spotlight.

"Chaos follows him around," says Butler, whose character keeps his native Scottish brogue and is tempted by a succession of hot suburban moms (Catherine Zeta-Jones, Uma Thurman, Judy Greer). "He's just a guy who's used to getting everything he wanted. At the end of the day it's not always the most fulfilling way to live. But it is a very seductive way to live."

It's not an entirely unfamiliar concept for a movie star.

"I've had fun along the way, but I've worked ‚?? listen, this was a second career for me," says Butler, noting his early professional life as a lawyer in Scotland. "And in my first career I was very unhappy‚?¶. But what I realize now is if you give me the right thing, I'm like a dog with a bone. I've put so much into my career, so much work, so much love."

Relationships notably buoy both fall films. "I don't know if it's every couple years I decide to do a family-oriented movie or if after a couple of years that suddenly grabs my attention," says Butler. "I think that at the end of the day I always have quite a sappy heart. And I'm a bit of a romantic and I get very touched, very emotional in movies, especially if they're done well."

Nor is the bachelor, who lives in Los Angeles and New York, immune to fatherly impulses.

Last week, Butler took his two 12-year-old nieces with him to the Chasing Mavericks premiere (his first kid-friendly film since 2008's Nim's Island). He can rattle off uncle-y trivia, quizzing his interviewer on the life span of flies and the pace of their wings. On set, Chasing Mavericks co-director Michael Apted noted how easily Butler bonded with children.. "I think he has a trick, which is he treats them as equals," says Apted. "He doesn't patronize them."

Playing a father "does make me think, 'Wow, maybe I could do this. Because I do love the qualities that you feel and the challenges that those roles present," says Butler.

Gregarious and charming in person, Butler, whom Apted calls " a very sociable animal" with colossal energy, "just likes to be in the middle of things and he likes a lot of stuff going on," the director says.

Muccino chuckled discussing Butler settling down. "He tends to be quite a consistent bachelor -- but I wouldn't be surprised if suddenly he would change his mind. I've seen it happen a lot."

Loves to take risks

Today Butler talks freely, brandishing a bruised index finger thanks to action on set of his recently wrapped White House thriller, Olympus Has Fallen. Although late to take his visiting nieces surfing in Malibu, he's generous with his time, sitting for an interview well over the allotted lunch hour and telling stories that travel from surfing in Hawaii with big-wave pro pal Laird Hamilton to getting banged up biking at night around redwoods in Northern California with three friends (and just one head lamp).

One can bike during the daytime, it feels charitable to point out.

"I'm not always the most common sense about these things," he says, grinning ruefully. "I was just determined that we were going to go biking."

That kind of enthusiasm can fill a room. Even after a 12-hour flight from London, Butler refuses to hide in the corners at his own premieres, gamely chatting up the after-party crowd (collapsing, he'll admit, practically shoes-on in his bed later).

It's partly why his directors love him. "I just love his enthusiasm, his love of what he's doing and his willingness to give anything a go," says Apted.

Almost anything. When a woman walks by in a pair of eyebrow-raising thigh-high leather boots, Butler's PG reaction is unexpectedly hilarious.

"Look at these boots that are coming through here," he says. "Look at this. Like, are you serious? The boots are getting longer and longer and they're starting earlier and earlier in the day."

(Butler simultaneously averts his gaze and ducks his head out of an invisible frame. He has learned the hard way about paparazzi catching him at inopportune moments.)

Although he doesn't read gossip stories about himself, Butler is protective of his reputation. When he checked into rehab in February for dependence on prescription painkillers, tabloids reported it was related to alcohol abuse. "That's when I say the stories can just get nasty," he says. "That bummed me out. But I haven't actually had a drink for 15 years. Nor have I had any wish to." (He also does not smoke.)

Even in today's micro-blogged world, he's picked up a talent for keeping his personal life private, and is rarely photographed with women he dates (although cameras did capture him a week ago in France with Romanian model Madalina Ghenea). "It's possible to do," he says. "But there's times when you want to go, 'You know what, I just want to be able to go out, sit out in the open and walk out in the streets. Of course, it gets harder and harder."

The open star even shares some of his regrets, including 2011's Machine Gun Preacher. "They advertised that as an action movie, but it was way more than that," he says. "I thought it was an important movie. Of all the movies I've done, that's the one that makes me saddest that more people didn't see it."

Today's outlook? Smooth sailing. In January he'll appear as a foul-mouthed leprechaun in Brett Ratner's "bizarre," celeb-packed Movie 43, and he's currently on the hunt for a black comedy or a "straight-up drama."